Plasma enhanced chemical vapor deposition method of forming a titanium silicide comprising layer

ABSTRACT

Chemical vapor deposition methods of forming titanium silicide including layers on substrates are disclosed. TiCl 4  and at least one silane are first fed to the chamber at or above a first volumetric ratio of TiCl 4  to silane for a first period of time. The ratio is sufficiently high to avoid measurable deposition of titanium silicide on the substrate. Alternately, no measurable silane is fed to the chamber for a first period of time. Regardless, after the first period, TiCl 4  and at least one silane are fed to the chamber at or below a second volumetric ratio of TiCl 4  to silane for a second period of time. If at least one silane was fed during the first period of time, the second volumetric ratio is lower than the first volumetric ratio. Regardless, the second feeding is effective to plasma enhance chemical vapor deposit a titanium silicide including layer on the substrate.

TECHNICAL FIELD

This invention relates to plasma enhanced chemical vapor depositionmethods of forming titanium silicide comprising layers.

BACKGROUND OF THE INVENTION

Conductively doped silicon regions are conventionally utilized assource/drain regions of field effect transistors and as other nodelocations in integrated circuitry. In fabricating integrated circuitryhaving such regions, insulative layers are typically fabricated over theregions and contact openings are formed therethrough to the regions.Conductive material is ultimately received within the openings and makeselectrical connection with the conductively doped source/drain or otherregions. Exemplary conductive materials include conductively dopedpolysilicon and other semiconductive materials, metals, and metalcompounds.

Refractory metal silicides, such as titanium silicide, have beenutilized as part of the conductive material, typically as an interfaceregion between the conductively doped silicon region and other overlyingconductive material. One prior art method of forming the titaniumsilicide is to deposit elemental titanium and thereafter heat thesubstrate to cause a reaction of the deposited titanium with underlyingsilicon to form the silicide. Alternately, deposition conditions can beselected such that the depositing titanium reacts with the silicon fromthe substrate during deposition to form the silicide. In eitherinstance, silicon is consumed from the underlying substrate diffusionjunction region in forming the silicide.

In certain applications, particularly in light of the ever-increasingdensity of circuitry being fabricated, it is highly undesirable for asignificant quantity of the underlying silicon of the junction to beconsumed. Accordingly, methods have been developed which prevent, or atleast reduce, underlying silicon consumption by providing a siliconsource other than or in addition to the silicon of the substrate forforming the silicide. One prior art method is to plasma enhance,chemically vapor deposit the silicide by combining a silane gas andTiCl₄ under suitable reaction conditions to form titanium silicide whichdeposits over the junction region with minimal if any consumption ofsubstrate silicon. Unfortunately, the wafer surface has been found onoccasion to become contaminated with particles in processes utilizingTiCl₄ and a silane as compared to primarily forming the silicide byreacting titanium with silicon of the substrate.

It was surmised that the particles which were undesirably forming on thewafers might be occurring during either or both of the actual titaniumsilicide deposition or after the deposition when the wafers were beingmoved into and out of the reactor chamber. While unclear, it wastheorized that the particle formation might be occurring from silaneand/or chlorine constituents adhering to the chamber sidewalls perhapsas a result of the deposition, or that chlorine was somehow undesirablybeing added to the chamber walls during a chamber cleaning which useschlorine intermediate each wafer deposition.

For example, one exemplary prior art processing intending to reduceparticle count employs a Cl₂ clean between titanium suicide depositionson separate wafers. For example, after a silicide deposition on onewafer within a reactor chamber, the wafer is removed from the chamber.Then, an argon flow of 500 sccm as a purge gas is flowed through thechamber. This is followed by a Cl₂ flow of 2,000 sccm for two seconds asa stabilizing step, with the Cl₂ flow then being continued at 2,000 sccmfor an additional 15 seconds. The intended effect of the Cl₂ clean is toremove titanium material which might undesirably adhere to the internalsurfaces of the chamber during the titanium silicide deposition. Uponcompletion of the Cl₂ cleaning step, an 8,000 sccm argon purge feedingis conducted to remove the chlorine. This is followed by a flow of Ar at8,000 sccm in combination with 1,000 sccm of He. He is lighter than Ar,and can facilitate chamber purging and cleaning, and also facilitatestemperature control within the chamber. Subsequently, another wafer isprovided within the chamber, and titanium silicide deposition isconducted.

The above-described cleaning process is typically conducted between eachsingle wafer deposition, and typically in the absence of plasma. Yetevery 10 to 20 wafer depositions, the chamber is also typicallysubjected to a plasma clean with Cl₂ to better clean/remove titaniumfrom the chamber walls. Further, every 5,000 or so wafer depositions,the whole system is subjected to an atmospheric/room ambient pressurewet clean and scrub (i.e., using NH₄OH, H₂O₂ and isopropyl alcohol invarious steps) whereby the whole system is cleaned out. The otherabove-described cleanings are typically conducted with the reactorchamber essentially at the deposition pressure and temperatureconditions.

The invention was principally motivated towards overcoming theabove-described surface defect issues, but is in no way so limited. Theinvention is only limited by the accompanying claims as literally wordedwithout limiting or interpretative reference to the specification, andin accordance with the doctrine of equivalents.

SUMMARY

The invention includes chemical vapor deposition methods of formingtitanium suicide comprising layers on substrates. In one aspect, asubstrate is provided within a plasma enhanced chemical vapor depositionchamber. In one implementation, TiCl₄ and at least one silane are firstfed to the chamber at or above a first volumetric ratio of TiCl₄ tosilane for a first period of time. The first volumetric ratio issufficiently high to avoid measurable deposition of titanium silicide onthe substrate. In another implementation, TiCl₄ is first fed to thechamber without feeding any measurable silane to the chamber for a firstperiod of time. Regardless, after the first feeding for the first periodof time, TiCl₄ and at least one silane are fed to the chamber at orbelow a second volumetric ratio of TiCl₄ to silane for a second periodof time. If at least one silane was fed during the first period of time,the second volumetric ratio is lower than the first volumetric ratio.Regardless, the second feeding is effective to plasma enhance chemicalvapor deposit a titanium silicide comprising layer on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic perspective view of a semiconductor waferfragment/section in process in a chemical vapor deposition reactorchamber in accordance with an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention encompasses a plasma enhanced chemical vapor depositionmethod of forming a titanium silicide comprising layer over a substrateusing a reactive gas comprising TiCl₄ and at least one silane. Thedescription and concluding claims include references to first and secondfeedings, ratios, etc. Such only indicate sequence with regard to therespective acts or nouns which they qualify, and in no way precludeother processing, including the stated acts, occurring intermediate thestated processings, nor do they preclude processings prior to the firststated processing or the last stated processing.

In accordance with an aspect of the invention, a substrate is positionedwithin a chemical vapor deposition reactor. By way of example only, thefirst substrate typically will comprise a semiconductor wafer or othersubstrate. In the context of this document, the term “semiconductorsubstrate” or “semiconductive substrate” is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above.

The chemical vapor deposition reactor includes plasma enhancement,either directly within the chamber or remote from the chamber. Theinvention was reduced to practice in a single wafer processor, althoughany other suitable reactor is contemplated, whether existing oryet-to-be developed. In a first and most preferred embodiment, TiCl₄ isfirst fed to the chamber without feeding any measurable silane to thechamber for a first period of time. Further most preferably, nothingother than TiCl₄ is fed to the chamber during the first period of time.In a 6.55 liter reactor, exemplary preferred flow rates for the TiCl₄are from 50 sccm to 150 sccm. Further preferably, the first feedingcomprises plasma generation within the chamber. An exemplary existingplasma enhanced chemical vapor deposition system usable in conjunctionwith the above-described process is the Centura Model #2658 availablefrom Applied Materials of Santa Clara, Calif. An exemplary preferredplasma generating power range is from 200 watts to 600 watts. Apreferred substrate temperature is from 600° C. to 700° C., with apreferred chamber pressure range being from 3 Torr to 6 Torr.Alternately but less preferred, the first feeding does not need tocomprise any plasma generation. The first period of time is preferablyno greater than 5 seconds, with no greater than 3 seconds being morepreferred.

In an alternate but less preferred embodiment, the first feedingencompasses feeding TiCl₄ and at least one silane to the chamber at orabove a first volumetric ratio of TiCl₄ to silane for a first period oftime. The first volumetric ratio is chosen to be sufficiently high toavoid measurable deposition of titanium silicide on the substrate. Anexpected minimum first volumetric ratio under typical depositionconditions is 500:1. More preferably, the first volumetric ratio is atleast 750:1, and even more preferably at least 1,000:1. Accordingly, inrespective preferred embodiments, the volumetric ratio of TiCl₄ is equalto or greater than these respective ratios. An exemplary silane is SiH₄,with silanes including more than one silicon atom, and organic silanes,also of course being contemplated. Regardless, exemplary preferredsilane flow rates are to provide at least the above-described preferredembodiment volumetric ratios. Additional gases beyond TiCl₄ and at leastone silane are also contemplated, but are believed to be less preferred.Where one or more silanes is/are fed during the first feeding, the firstfeeding might be at multiple volumetric ratios of TiCl₄ to all silaneduring the first period, or be at a substantially constant volumetricratio of TiCl₄ to all silane during the first period of time.

FIG. 1 depicts an exemplary embodiment chemical vapor deposition reactor10. A substrate 12 to be processed in accordance with an aspect of theinvention is shown positioned therein. Separate TiCl₄ and silane feedstreams are shown feeding to chamber 10. Such diagrammaticallyillustrates and represents one preferred embodiment whereby the TiCl₄and silane are fed to the chamber from separate injection ports duringthe first feeding. Most preferably, the TiCl₄ and silane are not mixedprior to feeding to the chamber, and not otherwise mixed prior to beingemitted to proximate the substrate within the chamber, during the firstfeeding.

Regardless of whether any silane is fed during the first feeding, afterthe first feeding, TiCl₄ and at least one silane are fed to the chamberfor a second period of time effective to plasma enhance chemical vapordeposit a titanium suicide comprising layer on the substrate. Plasmageneration can be direct within the chamber, or remote therefrom. Anysuitable gas components within the chamber, whether existing oryet-to-be developed, including TiCl₄ and a silane is contemplated. Asabove, an exemplary silane is SiH₄, with silanes including more than onesilicon atom, and organic silanes, also of course being contemplated. Byway of example only, one preferred process of forming a titaniumsilicide comprising layer includes plasma enhanced chemical vapordepositions at an exemplary power range of from 200 watts to 600 watts,a substrate temperature range of from 600° C. to 700° C. and a chamberpressure range of from 3 Torr to 6 Torr. Exemplary processing gasesinclude SiH₄ at from 0.5 sccm to 10 sccm, TiCl₄ at from 50 sccm to 150sccm, Ar at from 2,000 sccm to 6,000 sccm, He at from 1,000 sccm to2,000 sccm and H₂ at from 200 sccm to 10,000 sccm in a. 6.55 literchamber. Such exemplary processing can be conducted to plasma enhancechemical vapor deposit a titanium silicide comprising layer whichconsists essentially of titanium silicide. The second period of time forthe deposition is advantageously chosen to provide the selectedthickness deposition of a desired titanium silicide comprising layerover the substrate.

Typically and preferably, the second period of time is greater than thefirst period of time. Further, where at least one silane was fed to thechamber during the first feeding, the second or deposition feeding willinclude a second volumetric ratio of TiCl₄ to all silane which is lowerthan the first volumetric ratio.

The second feeding will occur at some selected chamber depositionpressure or pressure range, and at a selected substrate temperature ortemperature range. In one preferred aspect of the invention, the firstand second feedings are conducted at the same second feeding chamberdeposition pressure and substrate temperature conditions, and the TiCl₄flow rate during the first and second feedings is at a substantiallyconstant volumetric flow rate. Further, plasma conditions preferablyremain constant throughout. Alternately but less preferred, the flowrate of TiCl₄ during the first and second feedings can be at differentvolumetric flow rates.

A preferred although non-limiting effect is to provide a large quantityof TiCl₄ within the chamber, initially prior to the provision of adeposition quantity of silane such that the propensity of the silanewhen increased to deposition quantity conditions is to interact with theTiCl₄ at a much greater rate than with any components within the chamberrelative to either reacting therewith or adhering thereto. Thus, silaneadherence to chamber surfaces and as a source for subsequentcontamination is ideally minimized.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A plasma enhanced chemical vapor deposition method of forming atitanium silicide comprising layer over a substrate using a reactive gascomprising TiCl₄ and at least one silane, comprising: providing asubstrate within a plasma enhanced chemical vapor deposition chamber;first feeding TiCl₄ to the chamber without feeding any measurable silaneto the chamber for a first period of time; and after the first feedingfor the first period of time, second feeding TiCl₄ and at least onesilane to the chamber for a second period of time effective to plasmaenhance chemical vapor deposit a titanium silicide comprising layer onthe substrate.
 2. The method of claim 1 wherein the second feedingoccurs at selected chamber deposition pressure and substrate temperatureconditions, the first feeding also occurring at the selected secondfeeding chamber deposition pressure and substrate temperatureconditions.
 3. The method of claim 1 wherein the feeding of TiCl₄ duringthe first and second feedings is at a substantially constant volumetricflow rate.
 4. The method of claim 1 wherein the feeding of TiCl₄ duringthe first and second feedings is at different volumetric flow rates. 5.The method of claim 1 wherein nothing other than TiCl₄ is fed to thechamber during the first period of time.
 6. The method of claim 1wherein the first period of time is less than the second period of time.7. The method of claim 1 wherein the first period of time is no greaterthan 5 seconds.
 8. The method of claim 1 wherein the first period oftime is no greater than 3 seconds.
 9. The method of claim 1 wherein, thesecond feeding occurs at selected chamber deposition pressure andsubstrate temperature conditions, the first feeding also occurring atthe selected second feeding chamber deposition pressure and substratetemperature conditions; and the first period of time is less than thesecond period of time.
 10. The method of claim 1 wherein the firstfeeding comprises plasma generation within the chamber.
 11. The methodof claim 1 wherein the first feeding does not comprise plasma generationwithin the chamber. 12-40. (canceled)